(Adapted from the applicant's abstract) Dr. Blass is reapplying for an RSA since he is moving from Johns Hopkins University to Cornell University. The proposed research is concerned with the contribution of opioid peptides to behavioral development. It capitalizes on the facts that infusions of various solutions such as milk, sucrose, and corn oil into the mouths of rat or human infants causes marked calming hypalagesia. In rats, these effects are reversed by the opioid antagonist naltrexone. In contrast, comforting and antiociception caused by tactile stimulation is not opioid-mediated. There are four specific aims planned: (1) identify the loci in the gastrointestinal tract that mediate the antinociceptive and calming effects of each solution and their mechanism of action in rats; (2) identify the interactions between opioid and nonopioid mechanisms of calming and antinociception in rats, normal human infants, and infants born to opioid addicted mothers; (3) characterize the response patterns of drug addicted infants and post-term infants that present clinical and experimental profiles that are remarkably similar to those presented by addicted infants and; (4) further investigate the opioid bases of ingestive behavior. Taken together, these four goals are of theoretical and practical interest concerning the issue of opioid contributions toward development, mother-infant interactions, affect and addiction. These studies require the use of both animal and human subjects. The human studies will include about 200-300 healthy newborn infants annually as well as preterm infants and infants born to addicted mothers. These infants will be recruited from Tompkins Community Hospital in Ithaca and Wilson Memorial Hospital in Binghamton, N.Y. Video camera data will be obtained. The animal studies will require the use of about 2,000 infant Sprague-Dawley rats. Rats are used because of the extensive data available on their nervous and endocrine systems. These animals will be subjected to cannula implantation so that vocalization can be recorded. They will receive halothane anesthesia and will be euthanized by carbon dioxide inhalation.